Liquid crystal displays are commonly used as display devices for compact electronic apparatuses, because they not only provide good quality images but are also very thin. Because liquid crystal molecules in a liquid crystal display do not emit any light themselves, the liquid crystal molecules have to be lit by a light source so as to clearly and sharply display text and images. Therefore, liquid crystal displays usually require a backlight module.
Referring to FIG. 5, a typical backlight module 5 includes a reflective film 51, a light guide plate 52, a diffusion film 53 and a brightness enhancement film (BEF) 54 arranged in that order from bottom to top, and a light source 55. The light guide plate 52 includes a light incident surface 521, a light emitting surface 522 perpendicularly adjoining the light incident surface 521 and a bottom surface 523 opposite to the light emitting surface 522. The light source 55 is disposed adjacent to the light incident surface 521 of the light guide plate 52. The reflective film 51 is disposed below the bottom surface 523 of the light guide plate 52. The light source 55 includes a supporting plate 550 and a plurality of LEDs 551 disposed on the supporting plate 550.
In operation, light beams from the LEDs 551 enter the light guide plate 52 through the light incident surface 521, and penetrate in the light guide plate 52. A majority of the light beams emit out from the light emitting surface 522. A minority of the light beams emit out from the bottom surface 523 and reach the reflective film 51. These light beams are reflected by the reflective film 51 and are utilized again. These light beams enter the light guide plate 52 again through the bottom surface 523, and emit out from the light emitting surface 522. Then, light beams transmit through the diffusion film 53 and the BEF 54 and become uniform.
However, each of the LEDs 551 has a certain limited angle of divergence of light beams emitted therefrom. Therefore areas adjacent to the light incident surface 521 of the light guide plate 52 beyond the angles of divergence of the LEDs 551 may be relatively dark. That is, light beams emitted from the backlight module 5 may be non-uniform, and the performance of an associated LCD may be impaired.
What is needed, therefore, is a backlight module that can overcome the above-described deficiencies. What is also need is a liquid crystal display having such backlight module.